Thermoplastic resins such as polyester and polyamide, and thermosetting resins such as epoxy each have excellent moldability or processability, mechanical strength, and electrical characteristics for a general-purpose resin and an engineering plastic, and thus have been used in various fields including the fields of electricity and electronics. In addition, resin processed articles obtained by processing and molding those resins are required to be flame retardant in terms of safety for the purpose of preventing a fire at a high temperature. For example, specifications such as UL94 have been provided as flame retardance grades.
It is generally known that a halogen substance is effective in making such a resin processed article or the like flame-retardant. Flame retardance is imparted to the resin processed article or the like by adding a halogen-based flame retardant to a resin. The mechanism via which flame retardance is imparted by the halogen-based flame retardant is said to be as follows. That is, a halogenated radical is produced mainly by heat decomposition, and the produced halogenated radical captures an organic radical being a combustion source to stop the chain reaction of combustion, whereby high flame retardance is expressed.
However, a flame retardant containing a large amount of halogen compound may generate dioxin and the like depending on combustion conditions, so there has been a growing demand for reducing the amount of halogen in recent years from the viewpoint of reducing a load to the environment. Therefore, various non-halogen-based flame retardants each containing no halogen-based compound have been examined.
Inorganic flame retardants such as a metal hydrate and red phosphorus, triazine-based flame retardants derived from carbamide, organophosphorus-based flame retardants such as a phosphoric acid ester, and the like have been examined as such non-halogen-based flame retardants.
However, a metal hydrate such as aluminum hydroxide or magnesium hydroxide does not have a very high flame retardance imparting effect, so the metal hydrate must be blended with a large amount of resin. Therefore, the moldability of a resin is apt to deteriorate and the mechanical strength of a molded article to be obtained or the like is apt to reduce, thereby causing a problem in that applications of a usable resin processed article or the like are limited. In addition, red phosphorus is apt to inhibit electrical characteristics owing to insufficient dispersion, generate a dangerous gas, reduce moldability, and cause bleeding, although it has a high flame retardance effect.
On the other hand, for example, Patent Document 1 below discloses that a piperazine salt or alkylenediamine salt having 1 to 6 carbon atoms of an acidic phosphoric acid ester that has a phosphorinane structure is used as a flame retardant being an organophosphorus-based flame retardant such as a phosphoric acid ester.
In addition, Patent Document 2 below discloses a flame retardant for a resin mainly composed of a salt composed of an aromatic phosphoric acid ester such as monophenyl phosphate or monotolyl phosphate and an aliphatic amine such as piperazine.
Further, Patent Document 3 below discloses a phosphorus-containing phenol compound used as a flame retardant for providing a flame-retardant epoxy resin, which exerts an excellent flame retardance effect with a halogen-free flame-retardant prescription, providing a molded article excellent in physical properties such as heat resistance and water resistance and in adhesiveness in an electrical laminated plate application.
Further, Patent Document 4 below discloses an organic cyclic phosphorus compound having a bifunctional hydroxyl group particularly useful as a stabilizer for a polymer compound or as a flame retardant.
In addition, Patent Document 5 below discloses an organophosphorus compound having an allyl group as an unsaturated bond at a terminal of the compound.                Patent Document 1: JP 2002-20394 A        Patent Document 2: JP 2002-80633 A        Patent Document 3: JP 2002-138096 A        Patent Document 4: JP 5-331179 A        Patent Document 5: JP 2004-315672 A        